This application is based upon Japanese Patent Application No. Hei. 11-182454 filed on Jun. 28, 1999, No. Hei. 11-298997 filed on Oct. 21, 1999, and No. 2000-55923 filed on Feb. 28, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an angular position detecting apparatus, and in particular to an angular position detecting apparatus having an improved stator core arrangement.
2. Related Art
The angular position detecting apparatus having a rotor supporting a magnet and a stator supporting a detecting element is disclosed in JP-B2-2842482, JP-A-8-35809, WO 98/08060, U.S. Pat. No. 5,861,745 and DE 19634281 A1. For example, the angular position detecting apparatus detects an opening degree of a throttle valve (an opening degree of a throttle) of an internal combustion engine.
FIG. 22 shows a prior work by the inventor. As shown in FIG. 22, a stator core 12 is concentrically arranged at an inner side of a cylindrical rotor core 11, which integrally rotates with a throttle valve (not-shown). Two permanent magnets 13 having a circular arc shape are fixed to the inner side of the rotor core 11 so as to confront each other and sandwich the stator core 12. Each of the permanent magnets 13 is radially magnetized so that all of lines of magnetic force in the permanent magnets 13 are set to a radial direction. Incidentally, a gap portion 14 having a constant width for detecting a magnetic flux is formed at a center portion of the stator core 12 so as to open along a diametric direction. A detecting element 15 such as a Hall IC is provided in the gap portion 14. According to this structure, since a magnetic flux density passing through the gap portion 14 of the stator 12 (magnetic flux density passing through the detecting element 15) changes in proportion to the angular position of the rotor core 11, and since output of the detecting element 15 changes in proportion to the magnetic flux density, the angular position of the rotor core 11 (angular position of the throttle valve) is detected based on the output of the detecting element 15. As shown in FIG. 22, the gap portion 14 has a constant width and the detecting element 15 occupies only a part of the gap portion 14. Therefore, the detecting element 15 only detects a part of the magnetic flux which passes through the gap portion 14. Therefore, a powerful or large magnet, or a signal processing circuit having a high gain amplifier is required to achieve a sufficient signal indicating an output of the detecting element 15.
This invention has been conceived in view of the background thus far described and its first object is to provide an improved angular position detecting apparatus.
Its second object is to provide an improved angular position detecting apparatus out putting a sufficient level of signal from a detecting element.
Its third object is to provide an improved angular position detecting apparatus having a stator core for concentrating a magnetic flux into the detecting element.
Its fourth object is to provide a stator core arrangement for concentrating the magnetic flux into the detecting element without decreasing a detecting range.
According to one aspect of the present invention, a gap portion formed in a stator has a detecting portion which is a gap having a small distance and a large gap portion having a distance wider than the detecting portion for concentrating the magnetic flux into the detecting portion. Therefore, a detecting element arranged in the gap portion detects a concentrated magnetic flux and outputs a sufficient signal.